PERTHES DISEASE

PATHOGENESIS : Vascular supply of Femoral Head by 3 Arteries (At 4 mn of age): 

1. Metaphyseal Vessels
2. Lateral Epiphyseal Vessels in the Retinaculum
3. Artery in Ligamentum teres 

By age of 4 yrs, Metaphyseal supply diminishes to near zero, and Ligamentum teres artery becomes well developed after 7 yrs. So in between 4-7 yrs, the femoral head is mainly supported by Lateral Epiphyseal vessels which may get compromised by effusion following trauma or a non-specific synovitis.

Therefore, h/o Trauma (in50% cases) or Non-specific synovitis (irritable hip)

PATHOLOGY : 3 Stages :

1. Bone Death - Following one or more episodes of Ischemia, part of the bony femoral head dies. Looks normal on X-ray, but head stops enlarging
2. Revascularisation and Repair - New blood vessels enter the necrotic area and new bone is laid down on the dead trabecular, producing the appearance of Increased Density on Xray ; Some of the necrotic parts are resorbed and replaced by Fibrotic tissue producing the X-ray appearance of Epiphyseal Fragmentation
3. Distortion and Remodelling - Epiphysis may collapse and subsequent growth at head and neck will be distorted. Coxa plana ; Coxa magna ; femoral head is incompletely covered by acetabulum.

CLINICAL FEATURES:

A boy of 4-8 yrs presents with Pain and Limping

INVESTIGATIONS:

1. Earliest change seen on Radionuclide scanning : "Void" 
2. First Change on X-ray : Widened Joint Space
3. Increased density of femoral epiphysis 
4. Flattening, Fragmentation & Lateral Displacement of Epiphysis
5. Rarefaction and Broadening of the Metaphysis

DDx: "Irritable Hip"

1- TB Hip
2- Transient Synovitis
3- Morquio's Disease
4- Cretinsm
5-Multiple Epiphyseal Dysplasia (esp. if B/L)
6- SCD
7- Gaucher's Disease

"HEAD-AT-RISK SIGNS"

1- Calcification lateral to the Epiphysis
2- Lateral Subluxation of Femoral Head
3- Horizontal Proximal Femoral Physis
4- GAGE'S SIGN: V-shaped Radiolucency in the lateral portion of the epiphysis and/or proximal metaphysis.
5- Metaphyseal cysts